Determining the level of contaminants in a hydraulic system

Abstract

Apparatus and method for determining the level of particulate contamination within the fluid of a hydraulic system. System fluid is introduced through a non-return valve into a space where it is contained by a piston. The structure of the piston includes relatively-movable parts defining a restricted orifice to which fluid, having passed through a drilling in the piston, may escape to drain. When the piston is moved so as to tend to reduce the trapped volume, fluid is expelled from the volume through the drilling and clearance until the clearance becomes blocked by contaminants. The degree of contamination may then be derived from the distance that the piston has moved. The separate parts of piston structure are then relatively-moved to clear the orifice and allow the rest of the trapped fluid to escape, after which the orifice is reset and another volume of fluid introduced to be tested. The piston may be driven by reaction with the system fluid, or alternatively by means independent of that fluid. The specification describes alternative means for measuring the distance travelled by the piston, alternative piston structures to define the orifice, and alternative arrangements of the device as a whole relative to the hydraulic system as a whole.